Methods for generating lines for use in printers which have a raster output scanner and which are capable of printing a complete page line-wise with serially presented data are well known. Typically, front-end conversion systems connected to a workstation for inputting text and graphical data are required for laser printers. The laser printer includes a light beam which is modulated image-wise, and the modulated light beam is deflected line-wise by means of a polygonal mirror over a light-sensitive surface. In a known manner a latent image can be written to the light-sensitive surface by means of the modulated light beam. The latent image is thereafter developed in a known manner and transferred to a receiving material such as a sheet of paper.
In the front end the (coded) input text from a workstation is expanded with font data stored in a memory device, and the expanded text is also stored in the bit-map memory of the system. In addition, graphical data, for example of an original, obtained by means of a scanner can be fed to the workstation and bit-map memory.
The workstation is provided with a display by means of which the page to be printed can be composed. The layout of the page can be varied as required via the workstation. Special commands input via the workstation enable the front-end of the printer to generate various curves, e.g., straight lines parts, circles or arcs etc. and locate them in the bit-map memory.
The increasing resolution of raster output scanners makes them increasingly suitable for printing graphical information. The graphical information (line parts or the like) must be imaged on the raster of the raster output scanner. The imaging process comprise determining the collection of raster points to be activated. The activated raster points are thus written in a word-oriented bit-map memory. In view of the large number of raster points to be generated, rapid processing thereof is essential.
Because modern laser printers are capable of printing pages at high speed and with a high resolution, a front-end system will have to be capable of processing the data for said pages at high speed and presenting them to the printer.
U.S. Pat. No. 4,300,206 describes a raster printer in which data of any size and orientation can be printed on a page. A microprocessor receives a succession of coded character and control data. The coded character data are processed by the microprocessor one-at-a time in accordance with the control data and translated into character bit-map data and after that the microprocessor positions these data of character bit map into a strip buffer. However, because the described system operates in a sequential manner, it is a relatively slow system.
The following prior art is of general interest: Baker, et al. "Graphics Capabilities On A Laser Printer" p.17, Hewlett-Packard Journal (Nov. 1983); Sproull, "Using Program Transformations To Derive Line-Drawing Algorithms" AMC Transactions on Graphics, Vol. 1, No. 4 (Oct. 1982); Gordon, "Specialized High-Speed Electronics For Document Preparation Flexibility" p.30, Hewlett-Packard Journal, (June 1982); Bresenham, "A Linear Algorithm For Incremental Digital Display Of Circular Arcs," Communications of the ACM, Vol. 20. No. 2 (Feb. 1977); European Patent Application 0112025 and U.S. Pat. No. 4,031,519.
Accordingly, it is an object of the present invention to provide a method which can generate a line for high speed printing and high resolution printers.